Formation, Reactivity, and Photorelease of Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)] n + (trpy = 2,2′:6′,2′′-Terpyridine, L = 2-Phenylimidazo[4,5- f ]1,10-phenanthroline)

Formation, Reactivity, and Photorelease of Metal Bound Nitrosyl in[Ru(trpy)(L)(NO)]n+ (trpy ) 2,2′:6′,2′′-Terpyridine,L ) 2-Phenylimidazo[4,5-f]1,10-phenanthroline)

Somnath Maji,† Biprajit Sarkar,‡ Malay Patra,† Atanu Kumar Das,‡ Shaikh M. Mobin,†

Wolfgang Kaim,*,‡ and Goutam Kumar Lahiri*,†

Department of Chemistry, Indian Institute of TechnologysBombay, Powai, Mumbai 400076, India,and Institut für Anorganische Chemie, UniVersität Stuttgart, Pfaffenwaldring 55,D-70550 Stuttgart, Germany

Received November 2, 2007

Nitrosyl complexes with Ru-NO6 and Ru-NO7 configurations have been isolated in the framework of[Ru(trpy)(L)(NO)]n+ [trpy ) 2,2′:6′,2′′-terpyridine, L ) 2-phenylimidazo[4,5-f]1,10-phenanthroline] as the perchloratesalts [4](ClO4)3 and [4](ClO4)2, respectively. Single crystals of protonated material [4-H+](ClO4)4 · 2H2O reveal aRu-N-O bond angle of 176.1(7)° and triply bonded N-O with a 1.127(9) Å bond length. Structures were alsodetermined for precursor compounds of [4]3+ in the form of [Ru(trpy)(L)(Cl)](ClO4) · 4.5H2O and [Ru(trpy)-(L-H)(CH3CN)](ClO4)3 · H2O. In agreement with largely NO centered reduction, a sizable shift in ν(NO) frequencywas observed on moving from [4]3+ (1953 cm-1) to [4]2+ (1654 cm-1). The RuII-NO• in isolated or electrogenerated[4]2+ exhibits an EPR spectrum with g1 ) 2.020, g2 ) 1.995, and g3 ) 1.884 in CH3CN at 110 K, reflecting partialmetal contribution to the singly occupied molecular orbital (SOMO); 14N (NO) hyperfine splitting (A2 ) 30 G) wasalso observed. The plot of ν(NO) versus E°(RuNO6f RuNO7) for 12 analogous complexes [Ru(trpy)(L′)(NO)]n+

exhibits a linear trend. The electrophilic Ru-NO+ species [4]3+ is transformed to the corresponding Ru-NO2–

system in the presence of OH- with k ) 2.02 × 10-4 s-1 at 303 K. In the presence of a steady flow of dioxygengas, the RuII-NO• state in [4]2+ oxidizes to [4]3+ through an associatively activated pathway (∆Sq ) -190.4 JK-1 M-1) with a rate constant (k [s-1]) of 5.33 × 10-3. On irradiation with light (Xe lamp), the acetonitrile solutionof paramagnetic [Ru(trpy)(L)(NO)]2+ ([4]2+) undergoes facile photorelease of NO (kNO ) 2.0 × 10-1 min-1 and t1/2

≈ 3.5 min) with the concomitant formation of the solvate [RuII(trpy)(L)(CH3CN)]2+ [2′]2+. The photoreleased NOcan be trapped as an Mb-NO adduct.

Introduction

The research activities in the area of metal-nitrosylchemistry have grown extensively over the recent years withthe following primary perspectives: (i) understanding thebonding features of the noninnocent “NO” molecule onmetalation as it can occur either as cationic NO+, as radicalNO•, or as anionic NO-, depending on the electronic natureof the ancillary ligands associated with the M-NO frag-ment;1 (ii) variation of the extent of electrophilicity of theM-NO+ moiety and resulting reactivity profiles of M-NO+

with suitable nucleophiles;2 (iii) mechanistic studies of theM-NO•/O2 interaction in order to understand the biologicalautoxidation of free NO•;3 and (iv) the exploration ofselective photolytic cleavage of M-NO and the eventualtransfer of photoreleased “NO” to biologically relevant targetmolecules in order to develop alternative molecular devicescapable of functioning as efficient “NO” donors underbiological conditions.4

* To whom correspondence should be addressed. E-mail: [email protected] (W.K.), [email protected] (G.K.L.).

† Indian Institute of TechnologysBombay.‡ Universität Stuttgart.

(1) (a) Videla, M.; Jacinto, J. S.; Baggio, R.; Garland, M. T.; Singh, P.;Kaim, W.; Slep, L. D.; Olabe, J. A. Inorg. Chem. 2006, 45, 8608. (b)Singh, P.; Sarkar, B.; Sieger, M.; Niemeyer, M.; Fiedler, J.; Zalis, S.;Kaim, W. Inorg. Chem. 2006, 45, 4602. (c) Sieger, M.; Sarkar, B.;Zalis, S.; Fiedler, J.; Escola, N.; Doctorovich, F.; Olabe, J. A.; Kaim,W. Dalton Trans. 2004, 1797. (d) Roncaroli, F.; Baraldo, L. M.; Slep,L. D.; Olabe, J. A. Inorg. Chem. 2002, 41, 1930. (e) Slep, L. D.; Pollak,S.; Olabe, J. A. Inorg. Chem. 1999, 38, 4369.

Inorg. Chem. 2008, 47, 3218-3227

3218 Inorganic Chemistry, Vol. 47, No. 8, 2008 10.1021/ic702160w CCC: $40.75 2008 American Chemical SocietyPublished on Web 03/01/2008

The present work originates from the outlook of theaforesaid objectives using newly synthesized nitrosyl ruthe-nium derivatives [RuII(trpy)(L)(NO+)](ClO4)3 ) [4](ClO4)3

and [RuII(trpy)(L)(NO•)](ClO4)2 ) [4](ClO4)2 (trpy ) 2,2′:6′,2′′-terpyridine, L ) 2-phenylimidazo[4,5-f]1,10-phenan-throline). Although L has been of interest in the field ofcoordination chemistry for a number of years,5 only fewruthenium complexes of L and its derivatives have beenreported so far from different perspectives, mainly directedat studies of interaction with DNA.6

Results and Discussion

Synthesis and Characterization. The nitrosyl complex[RuII(trpy)(L)(NO)](ClO4)3 ) [4](ClO4)3 has been synthe-sized from the precursor [RuII(trpy)(L)Cl](ClO4) ) [1](ClO4)via the aqua form [RuII(trpy)(L)(H2O)](ClO4)2 ) [2](ClO4)2

or the acetonitrile solvate [RuII(trpy)(L)(CH3CN)](ClO4)2 )[2′](ClO4)2 and the nitro complex [RuII(trpy)(L)(NO2)](ClO4)) [3](ClO4) (Scheme 1). Attempts of direct synthesis of pure[4](ClO4)3 either from [1](ClO4), [2](ClO4)2 or [2′](ClO4)2

using NO gas or (NO)(BF4) have failed, thus, the stepwisesynthetic route via the nitro complex as shown in Scheme 1was followed. The isolated nitrosyl radical species [RuII-

(trpy)(L)(NO ·)](ClO4)2 ) [4](ClO4)2 has been prepared byreducing [4](ClO4)3 chemically using hydrazine hydrate.Electrochemical reduction of [4]3+ leads to the quantitativeformation of [4]2+ which can then be reversibly oxidized to[4]3+.

The diamagnetic compounds [1](ClO4), [2](ClO4)2, [2′]-(ClO4)2, [3](ClO4), and [4](ClO4)3 and the doublet species[4](ClO4)2 exhibit 1:1, 1:2, 1:2, 1:1, 1:3, and 1:2 conductivi-ties, respectively, and give satisfactory microanalytical data(see the Experimental Section). The electrospray mass spectraof [1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), [4](ClO4)3,and [4](ClO4)2 in CH3CN show molecular ion peaks centeredat m/z ) 665.94, 730.05, 729.93, 677.08, 730.72, and 730.42,respectively, corresponding to [1](ClO4) - ClO4+ (calcu-lated molecular mass: 666.07), [2](ClO4)2 - ClO4 - H2O+

(calculated molecular mass: 730.05), [2′](ClO4)2 - ClO4

- CH3CN+ (calculated molecular mass: 730.05), [3](ClO4)- ClO4+ (calculated molecular mass: 677.09), [4](ClO4)3

- 2ClO4 - NO+ (calculated molecular mass: 730.05), and[4](ClO4)2 - ClO4 - NO+ (calculated molecular mass:730.05), respectively (Figure 1).

The molecular structures of the cationic, partially proto-nated complexes in crystals of [1](ClO4) ·4.5H2O, [2′-H+]-(ClO4)3 ·H2O and [4-H+](ClO4)4 ·2H2O are shown in Figures2-4. Crystallographic parameters and selected bond dis-tances and angles are listed in Tables S1 and S2 (see theSupporting Information). In spite of numerous attempts, thequality of the crystals remained low; however, the bonddistances and angles match reasonably with similar com-plexes reported earlier.7 The lattice of [1](ClO4) ·4.5H2O

(2) (a) Roncaroli, F.; Videla, M.; Slep, L. D.; Olabe, J. A. Coord. Chem.ReV. 2007, 251, 1903. (b) McCleverty, J. A. Chem. ReV. 1979, 79,53. (c) Thiemens, M. H.; Trogler, W. C. Science 1991, 251, 932. (d)Feelisch, M., Stamler, J. S., Eds. Methods in Nitric Oxide Research;Wiley: Chichester, England, 1996. (e) Enemark, J. H.; Feltham, R. D.Coord. Chem. ReV. 1974, 13, 339. (f) Bottomley, F. In Reactions ofCoordinated Ligands; Braterman, P. S., Ed.; Plenum: New York, 1985;Vol. 2, p 115. (g) Bottomley, F. Acc. Chem. Res. 1978, 11, 158. (h)Ford, P. C.; Bourassa, J.; Lee, B.; Lorkovic, I.; Miranda, K.; Laverman,L. Coord. Chem. ReV. 1998, 171, 185. (i) Roncaroli, F.; Olabe, J. A.Inorg. Chem. 2005, 44, 4719. (j) Roncaroli, F.; Ruggiero, M. E.;Franco, D. W.; Estiu, G. L.; Olabe, J. A. Inorg. Chem. 2002, 41, 5760.(k) Forlano, P.; Parise, A. R.; Olabe, J. A. Inorg. Chem. 1998, 37,6406. (l) Bottomley, F. Coord. Chem. ReV. 1978, 26, 7.

(3) Videla, M.; Roncaroli, F.; Slep, L. D.; Olabe, J. A. J. Am. Chem. Soc.2007, 129, 278.

(4) (a) Halpenny, G. M.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.2007, 46, 6601. (b) Rose, M. J.; Olmstead, M. M.; Mascharak, P. K.J. Am. Chem. Soc. 2007, 129, 5342. (c) Rose, M. J.; Patra, A. K.;Alcid, E. A.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem. 2007,46, 2328. (d) Patra, A. K.; Rose, M. J.; Murphy, K. A.; Olmstead,M. M.; Mascharak, P. K. Inorg. Chem. 2004, 43, 4487. (e) Videla,M.; Braslavsky, S. E.; Olabe, J. A. Photochem. Photobiol. Sci. 2005,4, 75. (f) Zanichelli, P. G.; Miotto, A. M.; Estrela, H. F. G.; Soares,F. R.; Grassi-Kassisse, D. M.; Spadari-Bratfisch, R. C.; Castellano,E. E.; Roncaroli, F.; Parise, A. R.; Olabe, J. A.; de Brito, Alba Regina,M. S.; Franco, D. W. J. Inorg. Biochem 2004, 98, 1921. (g) Sauaia,M. G.; de.Lima, R. G.; Tedesco, A. C.; da Silva, R. S. Inorg. Chem.2005, 44, 9946. (h) Karidi, K.; Garoufis, A.; Tsipis, A.; Hadjiliadis,N.; den Dulk, H.; Reedijk, J. Dalton Trans. 2005, 1176.

(5) (a) Shavaleev, N. M.; Adams, H. A.; Weinstein, J. A. Inorg. Chim.Acta 2007, 360, 700. (b) Wei, Y.-Q.; Zhuang, B.-T.; Zhou, Z.-F.;Zhang, F. J. Mol. Struct. 2005, 751, 133.

(6) (a) Jiang, C.-W.; Chao, H. Polyhedron, 2001, 20, 2187. (b) Xiong,Y.; He, X.-F.; Zou, X.-H.; Wu, J.-Z.; Chen, X.-M.; Ji, L.-N.; Li, R.-H.; Zhou, J.-Y.; Yu, K.-B. J. Chem. Soc., Dalton Trans. 1999, 19. (c)Wu, J.-Z.; Ye, B.-H.; Wang, L.; Ji, L.-N.; Zhou, J.-Y.; Li, R.-H.; Zhou,Z.-Y. J. Chem. Soc., Dalton Trans. 1997, 1395. (d) Wu, J.-Z.; Li, L.;Zeng, T.-X.; Ji, L.-N.; Zhou, J.-Y.; Luo, T.; Li, R.-H. Polyhedron1997, 16, 103. (e) Uma Maheswari, P.; Palaniandavar, M. J. Inorg.Biochem. 2004, 98, 219. (f) Jiang, C.-W.; Chao, H.; Li, R.-H.; Li, H.;Ji, L.-N. J. Coord. Chem. 2003, 56, 147. (g) Chao, H.; Li, R.-H.; Jiang,C.-W.; Li, H.; Ji, L.-N.; Li, X.-Y. J. Chem. Soc., Dalton Trans. 2001,1920. (h) Zheng, K. C.; Deng, H.; Liu, X. W.; Li, H.; Chao, H.; Ji,L. N. J. Mol. Struct. 2004, 682, 225. (i) Li, J.; Xu, L.-C.; Chen, J.-C.;Zheng, K. C.; Ji, L.-N. J. Phys. Chem. A 2006, 110, 8174. (j) Tan,L.-F.; Chao, H.; Zhou, Y.-F.; Ji, L.-N. Polyhedron 2007, 26, 3029.

Scheme 1

Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)]n+

Inorganic Chemistry, Vol. 47, No. 8, 2008 3219

consists of two crystallographically independent molecules(Figure 2) which differ conspicuously in the relative orientationof the imidazole of L and the Ru-Cl bond. The acetonitrilecomplex has become protonated at the basic imine N of theimidazole ring to [RuII(trpy)(L-H+)(CH3CN)](ClO4)3 duringthe crystallization process from a CH3CN-benzene (1:1)

mixture over a period of 1 month (Figure 3). The linearity ofthe RuII-N(8)-O(1) bond (176.1(7)°) and the triple bondfeature of N(8)-O(1) (1.127(9) Å) support the electrophilicNO+ character in [RuII(trpy)(L-H+)(NO)](ClO4)4 ·2H2O; ad-ditional evidence from the νNO stretching frequency andE°(RuII-NO+/RuII-NO•) will be described later.7 In all cases,the ligand L forms a five-membered chelate ring with the metalion via the nitrogen donor centers of the phenanthroline unit.6b

Spectral Aspects. The 1H NMR spectra of diamagnetic[1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), and [4](ClO4)3

in (CD3)2SO (Figure S1, Supporting Information, and Ex-perimental Section) display severe overlap of the expected22 signals in the aromatic region between 7.0 and 10.5 ppm,11 resonances each from the trpy and the L ligand. Thechemical shift of the resonances varies slightly dependingon the monodentate ligands, Cl-, H2O, CH3CN, NO2

-, orNO+. The N-H proton of the imidazole ring of coordinatedL has only been observed for [1](ClO4) at 14.4 ppm.8 Theabsence of the N-H signal of the coordinated L in the othercomplexes can be attributed to rapid exchange.6j The signaldue to the CH3 group of coordinated acetonitrile in[2′](ClO4)2 appears at 2.38 ppm. While single crystals forX-ray diffraction were obtained in an imidazole-protonatedform for the complexes with the electrophilic CH3CN andNO+ monodentate ligands (see above), the dissolved speciesare identified as the imidazole forms with neutral L

Figure 1. ESI mass spectra of (a) [1](ClO4), (b) [2](ClO4)2, (c) [2′](ClO4)2, (d) [3](ClO4), (e) [4](ClO4)3, and (f) [4](ClO4)2 in CH3CN.

Figure 2. Molecular structure of the nonequivalent cations [Ru(trpy)(L)(Cl)]+ in the asymmetric unit of the crystal of [1](ClO4) ·4.5H2O.

Maji et al.

3220 Inorganic Chemistry, Vol. 47, No. 8, 2008

according to elemental analysis, molar conductivity, and1H NMR data.

The ν(ClO4-) vibrations are observed at 1096/623, 1089/

625, 1088/625, 1097/623, 1087/626, and 1091/628 cm-1 for[1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), [4](ClO4)3, and[4](ClO4)2, respectively. The typical Ru-NO2 frequenciesof [3](ClO4) appear at 1338 cm-1(asymmetric) and 1272cm-1 (symmetric). The νNO stretching frequency of [4](ClO4)3

at 1948 cm-1 is lower than that reported for analogouscomplexes RuII(trpy)(L′)(NO+) with L′ ) strongly π-acidicL3 ) 1952 cm-1, L2 ) 1957 cm-1, L1 ) 1960 cm-1 (Table1). However, it is much higher than that observed withstrongly σ-donating L10 ) 1858 cm-1 and L9 ) 1914 cm-1

and close to that found for moderately π-acidic L5 ) 1949cm-1 (Table 1). The observed νNO value of [4](ClO4)3 is thussuggestive of a moderately strong electrophilic character ofNO. On reduction of [4]3+ to [4]2+ the νNO frequency issubstantially reduced from 1948 (solid)/1953 (acetonitrilesolution) cm-1 to 1634 (solid)/1654 (acetonitrile solution)cm-1 (Figure 5). The large shift in νNO frequency, ∆ν )314(solid)/300(solution) cm-1, on moving from [4]3+ to [4]2+

agrees with a transformation of linear RuII-NO+, RuNO,6

to most likely bent RuII-NO•, RuNO.7,1c,2b,9

The complexes exhibit ruthenium(II) based metal to ligandcharge transfer (MLCT) transitions to π*(trpy) and π*(L)orbitals near 500 nm and ligand based multiple transitionsin the UV region (Figure 6, Table 2). The MLCT bandenergy in acetonitrile solution follows the order [1]+ (509nm) < [4]2+ (486 nm) < [3]+ (478 nm) < [2]2+ (462 nm) ≈[2′]2+ (461 nm) < [4]3+ (370 nm), depending on the relativestabilization of the dπ(Ru) level.7 The high energy shift ofthe MLCT band in [4]3+ implies a strong dπ(RuII) fπ*(NO+) back-bonding interaction. This has further beenevidenced in the observed short Ru-N8(NO) bond distanceof 1.766(7) Å (Table S2) and the relatively high νNO

frequency of 1948 cm-1. Electronic spectra of [2]2+ insolvents of different polarity show moderate variation (Table2, Figure 6).10

The complexes are found to be luminescent in frozensolution, the nitro derivative [3]+ displaying the strongestemission. The excitation of [1]+, [2]2+, [2′]2+, [3]+, or [4]3+

at the respective MLCT bands in EtOH:MeOH (4:1) glassat 77 K shows emission at λemis ) 705 nm (Φ ) 0.022) (Φcorresponds to the quantum yield at 77 K with reference to[Ru(bpy)3](PF6)2, Φ ) 0.3411), 675 nm (Φ ) 0.038), 597 nm(Φ ) 0.025), 623 nm (Φ ) 0.20), and 580 nm (Φ ) 0.11),respectively (Figure 6). The observed emissions are thought to

(7) (a) Mondal, B.; Paul, H.; Puranik, V. G.; Lahiri, G. K. J. Chem. Soc.,Dalton Trans. 2001, 481. (b) Chanda, N.; Paul, D.; Kar, S.; Mobin,S. M.; Datta, A.; Puranik, V. G.; Rao, K. K.; Lahiri, G. K. Inorg.Chem. 2005, 44, 3499. (c) Pipes, D. W.; Meyer, T. J. Inorg. Chem.1984, 23, 2466. (d) Maji, S.; Chatterjee, C.; Mobin, S. M.; Lahiri,G. K. Eur. J. Inorg. Chem. 2007, 3425. (e) Sarkar, S.; Sarkar, B.;Chanda, N.; Kar, S.; Mobin, S. M.; Feidler, J.; Kaim, W.; Lahiri, G. K.Inorg. Chem. 2005, 44, 6092. (f) Chanda, N.; Mobin, S. M.; Puranik,V. G.; Datta, A.; Niemeyer, M.; Lahiri, G. K. Inorg. Chem. 2004, 43,1056. (g) Dovletoglou, A.; Adeyemi, S. A.; Meyer, T. J. Inorg. Chem.1996, 35, 4120. (h) Hadadzadeh, H.; DeRosa, M. C.; Yap, G. P. A.;Rezvani, A. R.; Crutchley, R. J. Inorg. Chem. 2002, 41, 6521. (i) Singh,P.; Fiedler, J.; Záliš, S.; Duboc, C.; Niemeyer, M.; Lissner, F.; Schleid,T.; Kaim, W. Inorg. Chem. 2007, 46, 9254.

(8) (a) Maji, S.; Patra, S.; Chakraborty, S.; Mobin, S. M.; Janardanan,D.; Sunoj, R. B.; Lahiri, G. K. Eur. J. Inorg. Chem. 2007, 314. (b)Chakraborty, S.; Walawalkar, M. G.; Lahiri, G. K. J. Chem. Soc.,Dalton. Trans. 2000, 2875. (c) Hirsch-Kuchma, M.; Nicholson, T.;Davison, A.; Davis, W. M.; Jones, A. G. Inorg. Chem. 1997, 36, 3237.

(9) (a) Wanner, M.; Scheiring, T.; Kaim, W.; Slep, L. D.; Baraldo, L. M.;Olabe, J. A.; Zalis, S.; Baerends, E. J. Inorg. Chem. 2001, 40, 5704.(b) Haymore, B. L.; Ibers, J. A. Inorg. Chem. 1975, 14, 3060. (c)Gaughan, A. P.; Haymore, B. L.; Ibers, J. A.; Myers, W. H.; Nappier,T. F.; Meek, D. W. J. Am. Chem. Soc. 1973, 95, 6859. (d) Pandey,K. K. Coord. Chem. ReV. 1992, 121, 1.

(10) Mondal, B.; Walawalkar, M. G.; Lahiri, G. K. J. Chem. Soc., DaltonTrans. 2000, 4209.

Figure 3. Molecular structure of the trication [Ru(trpy)(L-H+)(CH3CN)]3+

in the crystal of [2′-H+](ClO4)3 ·H2O.Figure 4. Molecular structure of the tetracation [Ru(trpy)(L-H+)(NO)]4+

in the crystal of [4-H+](ClO4)4 ·2H2O.



originate from the triplet (3MLCT) excited states as observedin numerous ruthenium-polypyridine complexes.12

Redox Properties. The RuIII/RuII potentials of [1]+,[2′]2+, and [3]+ in CH3CN and of [2]2+ in H2O (Table 3)vary in the order of Cl- < H2O < NO2

- < CH3CN forthe monodentate ligand.7 The presence of RuIII in the

oxidized solutions has been established only for thecomplex [2′]3+ via its typical rhombic EPR spectrum (g1

) 2.444, g2 ) 2.201, g3 ) 1.851; Figure S2 in theSupporting Information). The potentials are in generalcomparable to those of the analogous [RuII(trpy)(L′)(X)]n+

complexes (X ) Cl-, NO2-, H2O, or CH3CN) and vary

(11) (a) Alsfasser, R.; Van Eldik, R. Inorg. Chem. 1996, 35, 628. (b) Chen,P.; Duesing, R.; Graff, D. K.; Meyer, T. J. J. Phys. Chem. 1991, 95,5850.

(12) (a) Kar, S.; Chanda, N.; Mobin, S. M.; Datta, A.; Urbanos, F. A.;Puranik, V. G.; Jimenez-Aparicio, R.; Lahiri, G. K. Inorg. Chem. 2004,43, 4911. (b) Sarkar, B.; Laye, R. H.; Mondal, B.; Chakraborty, S.;Paul, R. L.; Jeffery, J. C.; Puranik, V. G.; Ward, M. D.; Lahiri, G. K.J. Chem. Soc., Dalton Trans. 2002, 2097. (c) Juris, A.; Balzani, V.;Barigelletti, F.; Campagna, S.; Belser, P.; von Zelewsky, A. Coord.Chem. ReV. 1988, 84, 85.

Table 1. Reduction Potentials of the Ru(NO+)f Ru(NO•) Processand νNO Values for RuII(trpy)(L′)(NO)3+

L′ E298° [V]a ν(NO) (cm-1)b refs

L1 0.72 1960 7aL 0.49 1948 present workL2 0.45 1957 7bL3 0.45 1952 7cL4 0.40 1944 7dL5 0.36 1949 7eL6 0.34 1945 7fL7 0.33 1940 7bL8 0.31 1932 7bL9 0.02 1914 7gL10 -0.28 1858 7hL11 0.40 1957 7ia CH3CN/0.1 M Et4NClO4/SCE. b In KBr disk.

Figure 5. IR spectral changes for the conversion [4]3+f [4]2+ fromoptically transparent thin layer electrode (OTTLE) spectroelectrochemistryin CH3CN/0.1 M Bu4NPF6 with stepwise variation of the potential. Bandsbelow 1650 cm-1 arise from ring vibrations.

Figure 6. (a) Electronic spectra in acetonitrile of [1]+, [2]2+, [2′]2+, [3]+,[4]3+, and [4]2+. (b) Electronic spectra of [2]2+ in different solvents. (c) Emissionspectrum of [3](ClO4) in 4:1 EtOH-MeOH at 77 K.

Table 2. Electronic Spectral Data of Complexes

compound solvent λ [nm] (ε [M-1 cm-1])

[1](ClO4) acetonitrile 509(18611), 314(56016), 294(59038),276(82142), 236(53332)

[2](ClO4)2 acetonitrile 462(25718), 303(71232), 293(75163),282(97862), 276(100079), 222(60149)

methanol 479(13587), 310(57673), 277(81613),203(69519)

water 477(22789), 310(90825), 222(82525),310(90825)

acetone 477(22949), 323(53235), 312(18958),272(16284)

tetrahydrofuran 481(11975), 312(46252), 292(50562),281(58223), 235(33107)

dichloromethane 485(11975), 310(49245), 294(52556),280(65885), 225(39588)

dimethylformamide 497(15606), 316(66204), 296(70873),281(69875), 246(23627), 236(36276)

[2′](ClO4)2 acetonitrile 461(24924), 305(60845), 292(64340),281(67292), 244(37325), 221(55015)

[3](ClO4) acetonitrile 478(26062), 308(94246), 293(93837),279(100509), 220(74543)

[4](ClO4)3 acetonitrile 370(17921), 305(52234), 279(63725),276(67140), 222(55998)

[4](ClO4)2 acetonitrile 488(22696), 329(51801), 313(95981),303(102867), 293(108636),278(128496)

Maji et al.


according to the electronic aspects of L′.7 The trpy ligand-based reductions are observed in the range between -1.44and -1.99 V (Table 3).13

The nitrosyl based reductions involving the NO+ f NO•

and NO• f NO- conversion in [4]n+ appear at +0.49 and-0.26 V versus standard calomel electrode (SCE) (couplesI and II, Figure 7a, Table 3).7 The tricationic charge of [4]3+

facilitates the reversible reduction of the coordinated NO+

to NO• to occur at a rather high potential, and that effect iseven extended to the second one-electron reduction (NO•fNO-). The 0.75 V potential difference between the succes-sive NO centered reductions (couples I and II) gives rise toa comproportionation constant (Kc) of 1012.7 (RT ln Kc )∆E/0.059 (see ref 14) where ∆E ) 0.75 V) for theintermediate (radical) species [4]2+. This large Kc valuereflects the chemical stability of the intermediate whichfacilitated its isolation in the solid state. The EPR spectrumof [4]2+ exhibits g components at g1 ) 2.020, g2 ) 1.995,

and g3 ) 1.884 with an NO hyperfine splitting A2(14N) of30 G in CH3CN at 110 K (Figure 8). The pronouncedanisotropic profile of the spectrum arises from close lyingπ*(NO) orbitals (gav < 2) and from the partial contributionof the metal ion to the singly occupied molecular orbital(SOMO).1c,2b,9a,15 The similarity of the EPR parameters withthose observed and interpreted previously9a,15a is compatiblewith contributions of about 1/3 from the metal ion and 2/3fromthe NO group to the SOMO, implying a mixed resonanceformulation RuI(NO+)T RuII(NO•).9a The stepwise reduc-tion of coordinated trpy is observed at -1.17 and -1.43 V(couples III and IV, Figure 7a, Table 3). The RuII-NO+ fRuII-NO• reduction potentials for analogous complexes withdifferent ligands L′ (L1-L11, L) and the corresponding ν(NO)values (Table 1) follow a linear trend (Figure 7b).7

Reaction of [RuII(trpy)(L)(NO+)]3+ ([4]3+) with OH-.In spite of the relatively high ν(NO) stretching frequency of1948 cm-1 for [4]3+, suggesting facile nucleophilic attack,this complex ion is found to be persistent both in the solidand in CH3CN solution; it is only sparingly soluble in water.However, it undergoes facile transformation to the corre-sponding nitro derivative [3]+ under alkaline conditions inCH3CN. Due to the poor solubility of [4]3+ and the virtuallyinsoluble nature of the nitro derivative [3]+ in water (cf. itspreparation) the conversion had to be performed in CH3CN.The conversion process (eq 1)

[RuII(trpy)(L)(NO)]3+

[4]3++ 2OH-f [RuII(trpy)(L)(NO2)]

+

[3]++

H2O (1)

was monitored spectrophotometrically in the temperaturerange 303–323 K in CH3CN in the presence of aqueousNaOH solution ([4]3+, 0.22 × 10-4 M, and NaOH, 0.2 ×10-2 M; pseudo pH ∼ 10). The well-defined isosbestic points(Figure 9) are indicative of a clean conversion (1). Thepseudo-first-order rate constants (k [s-1]) at three differenttemperatures are: 2.02 × 10-4 (303 K), 3.97 × 10-4 (313K), 6.37 × 10-4 (323 K). The activation parameters (∆Hq/(13) (a) Mondal, B.; Puranik, V. G.; Lahiri, G. K. Inorg. Chem. 2002, 41,

5831. (b) Chanda, N.; Mondal, B.; Puranik, V. G.; Lahiri, G. K.Polyhedron 2002, 21, 2033. (c) Catalano, V. J.; Heck, R. A.; Ohman,A.; Hill, M. G. Polyhedron 2000, 19, 1049. (d) Catalano, V. J.; Heck,R. A.; Immoos, C. E.; Ohman, A.; Hill, M. G. Inorg. Chem. 1998,37, 2150. (e) Patra, S.; Sarkar, B.; Ghumaan, S.; Patil, M. P.; Mobin,S. M.; Sunoj, R. B.; Kaim, W.; Lahiri, G. K. Dalton Trans. 2005,1188. (f) Hedda, T. B.; Bozec, H. L. Inorg. Chim. Acta 1993, 204,103. (g) Deacon, G. B.; Patrick, J. M.; Skelton, B. W.; Thomas, N. C.;White, A. H. Aust. J. Chem. 1984, 37, 929.

(14) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.

(15) (a) Frantz, S.; Sarkar, B.; Sieger, M.; Kaim, W.; Roncaroli, F.; Olabe,J. A.; Zalis, S. Eur. J. Inorg. Chem. 2004, 14, 2902. (b) de Souza,V. R.; da Costa Ferreira, A. M.; Toma, H. E. Dalton Trans. 2003,458. (c) McGarvey, B. R.; Ferro, A. A.; Tfouni, E.; Bezerra, C. W. D.;Bagatin, I. A.; Franco, D. W. Inorg. Chem. 2000, 39, 3577. (d)Callahan, R. W.; Meyer, T. J. Inorg. Chem. 1977, 16, 574. (e) Diversi,P.; Fontani, M.; Fuligni, M.; Laschi, F.; Marchetti, F.; Matteoni, S.;Pinzino, C.; Zanello, P. J. Organomet. Chem. 2003, 675, 21.

Table 3. Redox Potentials of Complexesa,b

couple

compound RuIII/Ru IINO+ f

NO•NO• fNO- trpy reduction

[1](ClO4) 0.69(66) -1.53(54) -1.80(60)[2](ClO4)2

c 0.84(84) -1.59(53) -1.93(67)[2′](ClO4)2 1.22(95) -1.58(66) -1.99(62)[3](ClO4) 1.03(90) -1.44(94) -1.97(58)[4](ClO4)3 0.49(110) -0.26(154)d -1.17(72) -1.43(51)

a Potentials E298° [V] (∆E [mV]) versus SCE. b In CH3CN/0.1 MEt4NClO4. c In H2O/0.1 M NaClO4. d Quasi-reversible.

Figure 7. (a) Cyclic voltammogram of [4](ClO4)3 in CH3CN/0.1 MEt4NClO4. (b) Least-squares plot of E° [V] Ru(NO+)/Ru(NO•) versusν(NO)/cm-1 of twelve related complexes as listed in Table 1; ν(NO) [cm-1]) 1903 cm-1 + 107 cm-1/VE° [V], R ) 0.943.

Figure 8. Experimental (top) and computer simulated (bottom) EPRspectrum at 110 K of the radical complex [4]2+ generated by reduction of[4](ClO4)3 in CH3CN/0.1 M Bu4NPF6.



∆Sq) and equilibrium constant (K) values are calculated as44.24 kJ M-1/-169.54 J K-1 M-1, and 88, respectively. Thelarge negative ∆Sq value implies that the nucleophilic attackof OH- to the electrophilic NO+ center in [4]3+ takes placethrough an associatively activated process.7 The equilibriumconstant of 88 suggests that the nitro species [RuII(trpy)(L)(NO2)]+ ([3]+) exists as the main component.

The slope of the plot of pseudo-first-order rate constantvalues (k [s-1]), 2.02 × 10-4, 3.88 × 10-4, 9.97 × 10-4 inCH3CN ([4]3+, 0.22 × 10-4 M) at three different concentra-tions of OH- of 0.2 × 10-2, 0.4 × 10-2, and 1.0 × 10-2 M,respectively, yields the second order rate constant value of9.9 × 10-2 M-1 s-1. The estimated low rate constant valueof 9.9 × 10-2 M-1 s-1 for reaction 1 in CH3CN as comparedto the second-order rate constant (k [M-1 s-1]) valuesobtained for the analogous reported complexes [RuII-(trpy)(L′)(NO)]3+ (Table 1) in H2O L1, 6.94 × 105; L2, 4.7× 103; L5, 2.46 × 103; L6, 1.7 × 103; L8, 1.1 × 103 (assumingthat the concentration of OH- in H2O medium is 10-7 M)can be considered primarily due to the effect of thenonaqueous CH3CN medium. A similar effect of the non-aqueous CH3CN solvent on the rate constant value of reaction1 has also been observed in the case of [RuII(trpy)(L4)(NO)]3+

(k, 0.4 × 10-2 M-1 s-1).7d

Reaction of [RuII(trpy)(L)(NO•)]2+ ([4]2+) with O2. Thereaction of dioxygen with the metal bound nitrosyl group

MNO7 has been studied since long in the light ofunderstanding the biological NO autoxidation process.3

Mechanistic studies with a variety of transition metal-NOspecies suggest the formation of nitrato or nitrito complexeswhich proceeds via the intermediacy of an O-bound orN-bound peroxynitrite complex.16 Therefore, the reaction ofO2 with the nitrosyl species [RuII(trpy)(L)(NO•)]2+ ([4]2+)was followed spectrophotometrically at three different tem-peratures (298, 308, 318 K) in acetonitrile in the presenceof 0.1 M HClO4 (acetonitrile was used due to the poorsolubility of [4]2+ in water). Though [4]2+ is stable inacetonitrile under atmospheric conditions, in the presenceof a steady flow of dioxygen gas it slowly transforms to thecorresponding NO+ species [4]3+ (Figure 10) which can berepresented by eq 2.1a

2[RuII(trpy)(L)(NO•)]2+

[4]2++O2 + 2H+f

2[RuII(trpy)(L)(NO+)]3+

[4]3++H2O2 (2)

The isosbestic points in Figure 10 reveal the exclusiveinvolvement of two primary components ([4]2+/[4]3+) duringthe transformation process at the spectrophotometric timescale. The pseudo first order rate constants (k [s-1]) at threedifferent temperatures are the following: 5.33 × 10-3 (298K), 7.82 × 10-3 (308 K), and 11.96 × 10-3 (318 K). Theactivation parameters ∆Hq and ∆Sq are calculated as +29.3kJ M-1 and -190.4 J K-1 M-1, respectively. On the basisof the thermodynamic parameters, particularly the largenegative ∆Sq value, it may be proposed that the reactionproceeds through an associatively activated pathway involv-ing the initial binding of O2 with the M-NO fragment. Thesame reaction (eq 2) has also been tested using air insteadof oxygen gas under similar experimental conditions at 298K, and the estimated pseudo-first-order rate constant valueis found to be decreased significantly to 2.416 × 10-3 s-1.

Photocleavage of the RuII-NO Bond in [RuII(trpy)(L)(NO•)]2+ [4]2+ and Binding of Photoreleased NO withMyoglobin (Mb). The nitrosyl complex [RuII(trpy)(L)(NO+)]3+ [4]3+ was found to be stable in acetonitrile solutionunder ambient light conditions as well as under irradiationwith a Xenon 350 W lamp. However, on exposure to suchlight the deoxygenated acetonitrile solution of the one-electron reduced species, [RuII(trpy)(L)(NO•)]2+ [4]2+ un-dergoes facile photorelease of NO over a period of ∼30 minvia the selective cleavage of the Ru-NO bond and withconcomitant formation of the solvate species [RuII-(trpy)(L)(CH3CN)]2+ [2′]2+. The progression of the photo-cleavage of the RuII-NO• bond in [4]2+ was monitoredspectrophotometrically in CH3CN (Figure 11), and thepresence of isosbestic points suggests the direct transformationof [RuII(trpy)(L)(NO•)]2+ [4]2+ to [RuII(trpy)(L)(CH3CN)]2+

[2′]2+. The rate of the first-order photolytic release of NO (kNO)has been determined at 2.0 × 10-1 min-1 (t1/2 ≈ 3.5 min). Therate of photorelease of “NO” from the analogous complex[RuII(trpy)(L4)(NO•)]2+ (kNO [min-1] ) 4.4 × 10-3 and t1/2 ≈157 min7d) is 45 times slower than that estimated for [4]2+.

(16) Ford, P. C.; Lorkovic, I. M. Chem. ReV. 2002, 102, 993.

Figure 9. Time evolution of the electronic spectrum (5 min time intervals)of a solution of [Ru(trpy)(L)(NO)]3+ ([4]3+, 0.22 × 10-4 M) in the presenceof OH- (0.2 × 10-2 M; pseudo pH ∼ 10) in CH3CN at 313 K.

Figure 10. (a) Time evolution of the electronic spectrum (2 min timeintervals) of a solution of [Ru(trpy)(L)(NO)]2+ ([4]2+, 0.12 × 10-4 M) inCH3CN/0.1 M HClO4 under a steady flow of O2. The inset shows a steadydecrease of 488 nm absorption corresponding to [4]2+.

Maji et al.


This sort of photolytic cleavage of an M-NO bond maintainingthe overall integrity of the remaining part of the molecule isknown to have biological significance.4 Therefore, the feasibilityof binding the liberated “NO” to a biological target moleculesuch as myoglobin was explored.

When liberated “NO” from photolyzed [4]2+ in acetonitrilewas passed through the aqueous solution of reduced Mbunder deoxygenated condition the Mb-NO adduct wasspontaneously formed. This has been evidenced via thedevelopment of a characteristic intense band of Mb-NO atλmax ) 419 nm (Figure 12).17,18 The small absorption at 462nm in the spectrum of Mb-NO arises from the presence ofthe solvated species [RuII(trpy)(L)(CH3CN)]2+ [2′]2+ in thephotolyzed solution.

Conclusion

The present work demonstrates that the combination oftrpy and L coligands in the complex framework of Ru-(trpy)(L)(NO) facilitates the stabilization of the nitrosylgroup in both the NO+ and NO• redox states which arereversibly interconvertible via one-electron transfer. Thechanges in RuNO6,7 bonding for [4]3+ and [4]2+ are evidentfrom the ca. 300 cm-1 shift in the ν(NO) stretching fre-quency. The analysis of the EPR spectrum of [4]2+ suggestssignificant metal contributions to the NO-based SOMO. TheNO+ center in [4]3+ is sufficiently electrophilic to form the

corresponding nitro species [3]+ in the presence of OH-.The oxidation of the radical species [4]2+ to [4]3+ in thepresence of a steady flow of dioxygen proceeds through anassociatively activated pathway with a pseudo-first-order rateconstant of 5.33 × 10-3 s-1 at 298 K. In acetonitrile solutionthe Ru-NO bond in [4]2+ is susceptible to undergo photo-cleavage on exposure to light, forming the solvated species[2′]2+. The liberated NO can be scavenged by myoglobin.

Experimental Section

Materials. The precursor complex Ru(trpy)Cl319 and 2-phe-

nylimidazo[4,5-f]1,10-phenanthroline (L)20 were prepared as re-ported. 2,2′:6′,2′′-Terpyridine and silver nitrate were purchased fromAldrich. Other chemicals and solvents were reagent grade and usedas received. For spectroscopic studies HPLC grade solvents wereused.

Instrumentation. Solution electrical conductivity was checkedusing a Systronic conductivity bridge 305. Infrared spectra weretaken on a Nicolet spectrophotometer with samples prepared as KBrpellets. 1H NMR spectra were recorded using a 300 MHz VarianFT spectrometer with (CD3)2SO used as solvent. Cyclic voltam-metric and coulometric measurements were carried out using a PARmodel 273A electrochemistry system. A platinum wire workingelectrode, a platinum wire auxiliary electrode, and a saturatedcalomel reference electrode (SCE) were used in a standard three-electrode configuration. Tetraethylammoniumperchlorate (TEAP)was used as the supporting electrolyte and the solution concentrationwas ca. 10-3 M; the scan rate used was 50 mV s-1. A platinumgauze working electrode was used in the coulometric experiments.All electrochemical experiments were carried out under dinitrogenatmosphere. IR spectroelectrochemical studies were performed inCH3CN/0.1 M Bu4NPF6 at 298 K using an optically transparentthin layer electrode (OTTLE) cell21 mounted in the samplecompartment of a Perkin-Elmer 1760X FTIR instrument. The EPRmeasurements were made in a two-electrode capillary tube22 witha X-band Bruker system ESP300. UV–vis spectral studies wereperformed on a Perkin-Elmer Lambda 950 spectrophotometer. Theelemental analyses were carried out with a Perkin-Elmer 240Celemental analyzer. Electrospray mass spectra were recorded on aMicromass Q-ToF mass spectrometer. Magnetic susceptibility wasmeasured with a CAHN electrobalance 7550. Emission experimentswere performed using a Perkin-Elmer LS55 luminescence spec-trometer fitted with a cryostat.

Kinetic Experiment. For the determination of k in the conversionprocess of [RuII(trpy)(L)(NO+)]3+ ([4]3+)f [RuII(trpy)(L)(NO2)]+

([3]+) in acetonitrile in the presence of aqueous sodium hydroxidesolution (pH ∼ 10) the increase in absorbance (At) at 478 nmcorresponding to λmax of the nitro complex [3]+ was monitored asa function of time (t). AR was measured when the intensity changesleveled off. Values of pseudo first order rate constants, k, wereobtained from the slopes of linear least-squares plots of -ln(AR -At) against t. The activation parameters ∆Hqand ∆Sq were deter-mined from the Eyring plot.23

(17) (a) Fernandez, B. O.; Lorkovic, I. M.; Ford, P. C. Inorg. Chem. 2004,43, 5393. (b) Patra, A. K.; Mascharak, P. K. Inorg. Chem. 2003, 42,7363.

(18) SenGupta, N.; Basu, S.; Payra, P.; Mathur, P.; Lahiri, G. K.; Bhaduri,S. Dalton Trans. 2007, 2594.

(19) Indelli, M. T.; Bignozzi, C. A.; Scandola, F.; Collin, J.-P. Inorg. Chem.1998, 37, 6084.

(20) Liu, J. H.; Ren, X. Z.; Xu, H.; Huang, Y.; Liu, J. Z.; Ji, L. N.; Zhang,Q. L. J. Inorg. Biochem. 2003, 95, 194.

(21) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. 1991, 317,179.

(22) Kaim, W.; Ernst, S.; Kasack, V. J. Am. Chem. Soc. 1990, 112, 173.(23) Wilkins, R. G. The study of kinetics and mechanism of reaction of

Transition Metal Complexes; Allyn and Bacon: Boston, MA, 1974.

Figure 11. Time evolution of the electronic spectrum (2 min time intervals)of a solution of [Ru(trpy)(L)(NO)]2+ ([4]2+, 0.41 × 10-4 M) in CH3CNunder the exposure of light (Xe lamp, 350 W). The inset shows absorbanceversus time plot at 488 nm corresponding to [4]2+.

Figure 12. Absorption spectra of met-Mb, reduced Mb, and the Mb-NOadduct in water.



The pseudo-first-order rate constant for the conversion of[RuII(trpy)(L)(NO•)]2+ ([4]2+)f [RuII(trpy)(L)(NO+)]3+ ([4]3+) inCH3CN/0.1 M HClO4 solution in presence of steady flow ofdioxygen was determined from the single-exponential fitting of theplot of change in absorbance against time at λmax ) 488 nm. Theactivation parameters ∆Hq and ∆Sq were determined from theEyring plot.23

The first-order rate constant for the photorelease of NO from[RuII(trpy)(L)(NO•)]2+ [4]2+ was determined from a single-exponential fitting of the plot of change in absorbance against timeunder photolysis condition at λmax ) 488 nm in acetonitrile.

Photoreleased NO Trapping by Myoglobin. A solution of[4](ClO4)2 (3.0 mL) in acetonitrile was prepared in a quartz cuvettewith an optical path length of 1 cm and sealed with a rubber septum.The solution was deoxygenated by purging with nitrogen gas andphotolyzed for 30 min using a Xe 350 W lamp. The photoreleasedfree NO was allowed to pass through a solution of reduced myoglobinin water by a canula and the UV–vis spectrum was recorded.

Caution! Special precautions should be taken when handlingperchloric acid and organic perchlorates.

Synthesis of [Ru(trpy)(L)(Cl)](ClO4) [1](ClO4). The startingcomplex [Ru(trpy)Cl3] (100 mg, 0.23 mmol), 2-phenylimidazo[4,5-f]1,10-phenanthroline (L) (67.19 mg, 0.227 mmol), excess LiCl (54mg, 1.3 mmol), and NEt3 (0.4 mL) were taken in 25 mL of ethanol,and the mixture was heated at reflux for 8 h under a dinitrogenatmosphere. The initial greenish solution gradually changed to deeppurple. The solvent was then removed under reduced pressure. Thedry mass thus obtained was dissolved in a minimum volume ofacetonitrile, and an excess of a saturated aqueous solution of NaClO4

was added. The solid precipitate thus obtained was filtered off andwashed thoroughly with ice-cold water. The product was dried invacuo over P4O10. It was then purified by using a silica gel column.The complex [1](ClO4) was eluted by 2:1 CH2Cl2-CH3CN.Evaporation of the solvent under reduced pressure afforded pure[1](ClO4). Yield: 118.28 mg (68%). Anal. Calcd for C34H23-Cl2N7O4Ru (765.02) (found): C, 53.33 (53.01); H, 3.03 (2.96); N,12.81 (12.79%). Molar conductivity [ΛM (Ω-1 cm2 M-1)] inacetonitrile: 147. 1H NMR (CD3)2SO: δ )10.29 (d, 7.8 Hz, 1 H),9.30 (d, 8.1 Hz, 1 H), 8.85 (d, 8.1 Hz, 2 H), 8.72 (t, 5.1 Hz, 2.7Hz, 3 H), 8.59 (s, 1 H), 8.23 (m, 3 H), 7.94 (t, 7.2 Hz, 7.5 Hz, 2H), 7.64 (m, 4 H), 7.51 (m, 3 H), 7.23 (t, 6.6 Hz, 6.6 Hz, 2 H)ppm.

Synthesis of [Ru(trpy)(L)(H2O)](ClO4)2 [2](ClO4)2. The chlorocomplex [1](ClO4) (100 mg, 0.130 mmol) was taken in 25 mL ofwater and heated at reflux for 10 min. An excess of AgNO3 (221mg, 1.3 mmol) was added to the hot solution and the heating wascontinued for 1.5 h. It was then cooled and the precipitated AgClwas separated by filtration through a sintered glass crucible (G-4).The volume of the filtrate was reduced to 10 mL and an excess ofa saturated aqueous solution of NaClO4 was added. The solid aquacomplex [2](ClO4)2 thus obtained was filtered off, washed with ice-cold water and dried in vacuo over P4O10. Yield: 86.24 mg (78%).Anal. Calcd for C34H25Cl2N7O9Ru (847.01) (found): C, 48.18(47.97); H, 2.97 (3.11); N, 11.57 (11.27%). Molar conductivity [ΛM

(Ω-1 cm2 M-1)] in acetonitrile: 240. 1H NMR (CD3)2SO: δ ) 9.37(m, 1 H), 8.95 (m, 3 H), 8.76 (q, 6.3 Hz, 9.3 Hz, 8.7 Hz, 3 H),8.45 (m, 1 H), 8.32 (m, 3 H), 8.03 (m, 2 H), 7.64 (m, 7 H), 7.36(m, 2 H) ppm.

Synthesis of [Ru(trpy)(L)(CH3CN)](ClO4)2 [2′](ClO4)2. Thecomplex [2′](ClO4)2 was prepared following the same procedureas stated above for [2](ClO4)2, except using CH3CN as solventinstead of water. Yield: 84.03 mg (74%). Anal. Calcd forC36H26Cl2N8O8Ru (870.02) (found): C, 49.65 (49.77); H, 3.01

(2.98); N, 12.88 (12.56%). Molar conductivity [ΛM (Ω-1 cm2 M-1)]in acetonitrile: 236. 1H NMR (CD3)2SO: δ ) 9.96 (d, 4.8 Hz, 1H), 9.4 (d, 8.4 Hz, 1 H), 8.96 (d, 8.4 Hz, 2 H), 8.88 (d, 7.8 Hz, 1H), 8.78 (d, 8.4 Hz, 2 H), 8.5 (t, 8.4 Hz, 7.8 Hz, 2 H), 8.32 (d, 7.2Hz, 2 H), 8.08 (t, 6.9 Hz, 7.5 Hz, 2 H), 7.69 (m, 7 H), 7.34 (t, 6.3Hz, 6.3 Hz, 2 H) ppm.

Synthesis of [Ru(trpy)(L)(NO2)](ClO4) [3](ClO4). The aquacomplex [2](ClO4)2 (100 mg, 0.118 mmol) was dissolved in 25mL of hot water and an excess of NaNO2 (194 mg, 2.81 mmol)was added. The mixture was heated at reflux for 1.5 h. The deepred solution of the aqua species changed to deep orange during thecourse of reaction. The pure crystalline nitro complex precipitatedduring cooling to room temperature. The solid [3](ClO4) thusobtained was filtered off, washed with ice-cold water and dried invacuo over P4O10. Yield: 76.91 mg (84%). Anal. Calcd forC34H23ClN8O6Ru (776.04) (found): C, 52.57 (53.17); H, 2.99 (2.99);N, 14.44 (14.44%). Molar conductivity [ΛM (Ω-1 cm2 M-1)] inacetonitrile: 127. 1H NMR (CD3)2SO: δ ) 10.01 (d, 5.1 Hz, 1 H),9.32 (d, 8.1 Hz, 1 H), 8.85 (t, 8.4 Hz, 6.9 Hz, 3 H), 8.71 (d, 8.1Hz, 2 H), 8.40 (m, 4 H), 8.01 (t, 8.1 Hz, 7.8 Hz, 2 H), 7.59 (m, 7H), 7.28 (t, 6.6 Hz, 6.0 Hz, 2 H) ppm.

[Ru(trpy)(L)(NO)](ClO4)3 [4](ClO4)3. Concentrated HNO3 (2mL) was added dropwise at 273 K on the solid nitro complex[3](ClO4) (100 mg, 0.129 mmol) under stirring condition. To thepasty mass thus obtained was added an ice-cold concentrated HClO4

solution (6 mL) with constant stirring. Addition of a saturatedaqueous NaClO4 solution resulted in a yellow precipitate whichwas filtered and washed with about 4 mL of ice-cold water andthen dried in vacuo over P4O10. Yield: 101.22 mg (82%). Anal.Calcd for C34H23Cl3N8O13Ru (957.94) (found): C, 42.59 (41.39);H, 2.42 (2.42); N, 11.69 (10.99%). Molar conductivity [ΛM (Ω-1

cm2 M-1)] in acetonitrile: 314. 1H NMR (CD3)2SO: 9.83 (d, 5.4Hz, 1 H), 9.66 (d, 9.0 Hz, 1 H), 9.28 (m, 3 H), 9.16 (t, 6.9 Hz, 9.3Hz, 1 H), 9.04 (d, 8.1 Hz, 2 H), 8.70 (t, 8.1 Hz, 5.1 Hz, 1 H), 8.49(t, 7.8 Hz, 8.1 Hz, 2 H), 8.33 (d, 7.2 Hz, 2 H), 7.89 (m, 3 H),7.63(m, 6 H) ppm.

Synthesis of [Ru(trpy)(L)(NO)](ClO4)2 [4](ClO4)2. The nitrosocomplex [4](ClO4)3 (100 mg, 0.116 mmol) was dissolved in 5 mLof CH3CN, and excess hydrazine hydrate was added under stirringover a period of 5 min under a dinitrogen atmosphere. The stirringwas continued at room temperature for further 0.5 h. The initiallyyellow solution of [4](ClO4)3 changed to red-brown. The solventwas then removed under reduced pressure and the solid mass thusobtained was washed with little ice-cold water and then dried invacuo over P4O10. Yield: 65.4 mg (73%). Anal. Calcd forC34H23Cl2N8O9Ru (859.00) (found): C, 47.51 (47.42); H, 2.70(2.81); N, 13.04 (12.93%). Molar conductivity [ΛM (Ω-1 cm2 M-1)]in acetonitrile: 215. Magnetic moment, µ(B.M.) at 298 K ) 1.83.For other physical characterizations, see main text.

Crystallography. Single crystals of [1](ClO4) ·4.5H2O, [2′-H+]-(ClO4)3 ·H2O and [4-H+](ClO4)4 ·2H2O were grown by slowevaporation of the respective 1:1 acetonitrile-benzene solutionsat 298 K in air. X-ray data were collected using an OXFORDXCALIBUR-S CCD single crystal X-ray diffractometer. Thestructures were solved and refined by full-matrix least-squarestechniques on F2 using the SHELX-97 program.24 The absorptioncorrections were done by the multiscan technique. All data werecorrected for Lorentz and polarization effects, and the nonhydrogenatoms were refined anisotropically. Hydrogen atoms were includedin the refinement process as per the riding model.

Acknowledgment. Financial support received from theDepartment of Science and Technology (DST) and Council of

Maji et al.


Scientific and Industrial Research (CSIR), New Delhi (India),the DAAD, the DFG, and the FCI (Germany) is gratefullyacknowledged. Special acknowledgement is made to theSophisticated Analytical Instrument Facility (SAIF), IndianInstitute of Technology, Bombay, for providing the NMRfacility.

Supporting Information Available: Crystallographic parametersof [1](ClO4) ·4.5H2O, [2′-H+](ClO4)3 ·H2O, and [4-H+](ClO4)4 ·2H2O (Table S1); selected bond distances and angles of [1](ClO4) ·4.5H2O, [2′-H+](ClO4)3 ·H2O, and [4-H+](ClO4)4 ·2H2O (Table S2);1H NMR spectra of [1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), and[4](ClO4)3 in (CD3)2SO (Figure S1); EPR spectrum of [2′]3+ in CH3CN(Figure S2). This material is available free of charge via the Internetat http://pubs.acs.org.

IC702160W(24) Sheldrick, G. M. Program for Crystal Structure Solution and Refine-

ment; Universität Göttingen: Göttingen, Germany, 1997.



Documents

Formation, Reactivity, and Photorelease of Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)] n + (trpy = 2,2′:6′,2′′-Terpyridine, L = 2-Phenylimidazo[4,5- f ]1,10-phenanthroline)